Power supply circuit means



2 Sheets-Sheet l Aug, 9,1949. c. J. MULLIN POWER SUPPLY CIRCUIT MEANS Filed May 5, 1945 Aug. 9, 1949.

Filed May 5; 1945 2 Sheets-Sheet 2 s,= POWER SWITCH T s CONTACTS OF VACUUM RELAY Y L STARTING INDUCTOR AND RE- LAY COIL-APPROXIMATELY S 6' O.| henry AND 25 ohms. (MINI' MUM In DucTANcE REQUIRED j: g R TO OPERATE CONTACTS,

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atentecl Aug. 9, 1949 POWER SUPPLY CIRCUIT MEANS Charles J. Mullin,

the

Arlington, United States of America as represented Mass., assignor to by the Executive Secretary of the Oflice of Scientific Research and Development Application May 3, 1945, Serial No. 591,723

1 Claim.

This invention relates to power supply means for starting and operating gaseous arc tubes and in particular to a method and apparatus for projection in which the power supply and tube are employed to facilitate plotting operations.

It has been found that information obtained by radar may be combined advantageously with the operation of a navigational instrument of the type referred to as Dead Reckoning Tracer. To do this it is necessary to carry out plotting operations which require a projection apparatus furnished with an intense source of illumination.

In one aspect the invention comprises the combination with projection apparatus, of a specially constructed gaseous arc tube which furnishes a point of light, and a power supply for starting and operating the gaseous arc tube. The tube is referred to as a point source tube and it is a characteristic of such a tube when used with the projection apparatus that a relatively high voltage is required to fire the gaseous arc and start operation of the tube.

I have discovered a novel power supply circuit for a gaseous arc tube by means of which I am enabled to develop a sudden inductance kick or high voltage which is suitable particularly for starting operation of the tube. An important feature of the power supply is the combination with the gaseous arc tube of an inductance element and switch means for very abruptly terminating the flow of current through the inductance element. This is a, very convenient arrangement for obtaining a high starting voltage from the low voltage D. C. source available in the Dead Reckoning Tracer installed on board a ship.

Another feature consists in the fact that the power supply is capable of delivering a, high starting voltage which is nevertheless subject to variation in accordance with the starting requirements of the tube in either a hot or cold state.

Another feature is the provision in the power supply circuit of means by which the high voltage remains in effect only for a period long enough to start the tube. Thereafter the tube operates on a low D. C. voltage.

Still another feature consists in the assembly of the power supply elements in an exceedingly compact and relatively small unit, which may be mounted conveniently within the housing of the Dead Reckoning Tracer or at points outside the housing.

The power supply and tube circuit also are characterized by positive safety features which preclude possible injury under various conditions which may arise during use of the tube with the projector.

The invention is further characterized by projection apparatus combined with a gaseous arc tube which is formed with a novel cathode and anode plate construction to provide a relatively large projection angle. This characteristic, in conjunction with the power supply starting circuit, makes it possible to project a relatively large image on a relatively small projection distance where the use of a lens system would be unsatisfactory. As available projection distance in a Dead Reckoning Tracer is limited by the location of its plotting surface in relation to the point at which the projector is required to be mounted, this is an important improvement.

In the accompanying drawings:

Fig. 1 is a fragmentary perspective view of a Dead Reckoning Tracer in which is mounted the projection apparatus and power supply means of the invention;

Fig. 2 is a cross-sectional view of the Dead Reckoning Tracer;

Fig. 3 is a detail view of projected subject matter;

Fig. 4 is a perspective view of the gaseous arc tube of the invention;

Fig. 5 is a schematic circuit diagram further illustrating the power supply means; and

Fig. 6 is another schematic circuit diagram indicating a modification of the invention.

The drawings illustrate a preferred embodi ment of the invention in which a point source tube and a power supply for starting and operating the tube are combined with a Dead Reckoning Tracer to carry out desired plotting operations. It should be understood, however, that the invention is not limited to this specific application and combination, and may be practiced in other forms, and in particular the power supply means may be utilized for operating gaseous arc tubes in various applications.

In the preferred embodiment noted, numeral 2 denotes a box-like structure which is generally referred to as a Dead Reckoning Tracer. (Fig. 1). The construction of this navigational instrument forms no part of the present invention but a brief description is believed to be desirable in order to understand clearly the importance of the projector and power supply and their relation to the Dead Reckoning Tracer.

The structure 2 is formed with a chamber which is closed by means of a hinged cover. The cover has been iragmentarily indicated in Fig. 1 of the drawings, and consists of a frame 4 in which is secured a glass panel 6 which serves as a plotting surface for the instrument. Within the chamber is located some form of projection apparatus. As employed ordinarily, the Dead Reckonin Tracer is provided with an incandescent light source which serves as a projector and is adjusta'bly mountedon a threaded shaft Ill, pivotally supported between the sides of the member 2. The lighting unit is enclosed so that it sends out a small beam of light and is in turn electrically connected with another conductor bar i i.

Movement of the lighting unit in directions both transversely and longitudinally of the boX member 2 is provided by means of driving mech anism located at one end of the box member 2 and acting through shafts I 6 and 18. This conventional type of projector functions to project a small dot on the plotting surface of the Dead Reckoning Tracer, and the driving mechanism is so controlled that the dot is caused to indicate information relating to the course which is being followed by the ship in which the Dead Reckoning Tracer is mounted. 1

Inaccordance with the invention, I provide an improved projector 20 which may be mounted on the shaft If! in the chamber of a Dead Reckoning Tracer in the-same way as a conventional type of projector would be. The projector 20 includes an luminum case of cylindrical shape, a glass dial 22 located at the top of the case, and a point source tube 24 (Fig. 4), mounted in the base of the aluminum casing. The dial member consists ofsubject matter representing a polar coordinate system represented in Fig. 3. This subject matter is projected onto the plotting surface of the Dead Reckoning Tracer and moves about in much the samemanner as the dot utilized in a conventional form of Dead Reckoning Tracer.

The point source tube 24 is a gaseous arc tube having a specially constructed cathode consisting of a hollow cylinder 28 of tantalum containing zirconiumoxide. A very small area only of the zirconium oxide is left uncovered at the upper end of the cylinder 28. This area in operation is bombarded electronically to provide a "point or source of intense light.

The anode of the tube consists of a plate 32 formed with anorifice 30 which is located very close to the exposed area of zirconium oxide so that there is obtained a suitable angle of divergence of light.- An angle of 120 is cited as an example of a preferred arrangement, although otherv angles may be employed. Numeral 33 refers to side walls extending right angularly away from the plate 32. These side walls function as additional heat transfer means and are desirable to take care of the fact that the more compact arrangement of the electrodes requires a faster dissipation of heat.

The brightness of the image at the plotting surface obtained from a point source tube of the character described can be controlled in the usual way by adjusting the current passing through the tube. It will be noted that by means of such an intense point of light and the relatively large angle of divergence of light from the new arrangement of anode and cathode, it becomes possible to provide a relatively large size projection in a very limited projection distance. This is especially desirable in the use of a Dead Reckoning Tracer since there is need for an exceedingly large projected image which will permit a number. of plotting operations to be carried out simultaneously. and the Dead Reckoning Tracer is characterized by a very limited projection distance between the projector carriage and the plotting surface which cannot be readily changed.

In Fig. 6 I have indicated a schematic circuit diagram comprising a preferred embodiment of a power supply arrangement for starting and operating the gaseous arc tube 24. The power supply voltage is proportional to its load and the essential parts are: a source of low D. C. voltage obtained from a D. C. line, or an A. C. operated power supply, connected to the gaseous arc tube; an inductance member connected into the circuit at one side of the tube; and a fast breaking switch connected between the inductance element and. the source of D. C. voltage.

As may be observed from an inspection of Fig. 6, I have indicated a source of low D. C. voltage at the lower right-hand side of the diagram, across which is connected a switch S-l. A second switch S2 is indicated at the left hand side of the diagram which is in turn controlled by a swltch'S-..3 as noted. L denotes an induc-v tance which may consist of a coil of wire wound about an iron core in the usual manner, and the gaseous arc tube 24 is indicated at the upper part of the diagram.

The circuit further includes a condenser C and resistances R1, R2,,Ra, R4. Suitable values for these and other circuit components have been noted in the drawings. These values are intended to illustrate one workable form of the invention and should not be regarded in any limiting sense. In addition, it should be noted that the wire of the inductance coil L; should be large enough to carry the current which is to be broken, and the coil should be properly-insulated so as not to break under the starting voltage.

In operation the switchS.-l is closed, making available a source of D. C. voltage. In order for current to flow in the circuit, the switch 5-3 is closed, as by depressing a push button, and a closed circuit is formed through the relay L--l and the resistance R4. The relay in turn operates the switch S12 in the usual manner, which forms a closed circuit through the inductance coil L.

When the push button starting switch S-3 is released, the arm of the vacuum relay moves away from the normally open contact of S2, and by reason of the vacuum, flow of current through the inductance coil L is very abruptly interrupted. The sudden break of the current through the inductance coil L produces a relatively high voltage of 1200 volts or more across the coil. This voltage is applied across the electrodes of the gaseous arc tube and serves as a starting voltage for firing the gaseous arc. The are tube is then operated from the low D. C. voltage since operation of the tube closes a circuit from the low D. C.-voltage source through S-,- 2, then to the tube and back to the ground. The relay thus serves to control also the second low voltage operating circuit.

Interrupt n flow of current in a circuit such as that shown in Fig. 6 develops a voltage across the terminals of theinductance coil L. The size of the voltage produced depends on several factors, including how fast the current is interrupted; the size of the current stopped; the size of the conductors of the coil; and the amount of the impedance across the coil.

In practice, only the first of these factors can be increased materially and the operation of the power supply circuit of the invention is based 599 1 fi. PPEQ IQ .9? YZ 3 2? 41 9. i t r u n flow of current through the inductor L, thereby to create a sudden inductance kick or high voltage across L. This voltage is applied across the electrodes of the gaseous arc tube 2 2, thus inducing a rapid flow of ions which com-bard the cathode terminal or electrode, and fire the tube.

As an example of one type of fast breaking switch, I have illustrated the vacuum relay switch S2. The sudden break obtained with the vacuum switch results from the fact that as the switch contacts separate, there are practically no ions present to continue flow of current between the contacts.

Another feature is the manner in which voltage is developed. It will be seen that the voltage developed across the coil L is dependent upon the impedance across the coil, and attention is directed to the fact that the impedance is the tube itself. As a result of this, there is available a power supply whose voltage is proportional to the load, and the voltage developed is just the voltage required to fire or start the tube, as distinguished from ordinary power supply arrangements which deliver, within limits, approximately the same voltage under any condition.

It should also be observed that the tube offers a difierent impedance when hot from the impedance which is present when the tube is cold.

Thus, to fire the arc and start operating the tube in a cold state, high voltage is necessary, If, however, the tube were in a hot state and required to be started, such as may well occur, substantially different voltage would be desired. It is essential that the voltage developed should not exceed the exact value required to start the tube. This is so for the reason that should higher voltages be present, a great deal more insulation would be needed. Also the higher voltage is dangerous and may well injure the cathode. Similarly, the high voltage should not be on for longer than necessary because there may result injury to the cathode and possibly it may be dangerous.

The power suply of the invention, therefore,

due to the fact that its voltage is proportional to load, provides just the required voltage, either for a hot or cold tube, maintains this voltage, whatever it may be, in efiect for a short time only, and then provides for low voltage operation. The

various disadvantages above noted which are r common to the ordinary type of power supply are thus avoided.

If desired, the power supply arrangement may be modified in various respects. For example, in Fig. 5 I have indicated an automatically-operated circuit by means of which only one switch is required to be closed to fire the tube 24 and thus operate it on a low voltage circuit. Upon closing switch S--l, current flows through L back to the ground. L functions as both an inductor and a relay coil. In its latter capacity L operates the arm of switch S2, opening the circuit and developing a high voltage across the coil to fire the tube in the manner already described. Circuit component values for this type of power supply are indicated on the drawings.

The combination of a point source tube and the power supply with a Dead Reckoning Tracer in the manner described, has been found to be highly satisfactory in carrying out important determinations involved in tactical plotting. In particular, the combination permits a number of plotting operations to be carried out simultaneously by reason of the large plotting area resulting from the large size projected image. In this connection, it should be noted that the tube and power supply assembly has been particularly adapted to the size limitations of a Dead Reckoning Tracer, and these elements are assembled in a compact and convenient manner. The design of the gaseous arc tube is also carried out so that substantially increased angle of divergence is obtained in the projecting operation,

Attention is again directed to various advantages present in the power supply circuit. Thus, for example, since starting voltage developed across the inductance coil is dependent upon the impedance across the coil, and since impedance is the tube itself, the voltage developed is always just that voltage required to start the tube. For the same reason, if one places body resistance across the starting circuit, no serious harm can be done. The two-contact switch makes it possible to bypass the coil after the tube has started. Thus the coil need not carry current after starting and may be of a smaller size.

By inclusion of a standard type rectifier and filter, the power supply circuits described above 5 may be operated from an A. C. power source.

Having thus described my invention, what I claim is:

An electrical system comprising an electrical gaseous discharge tube; a source of voltage for said tube; and a starting and operating circuit for said tube; said source of voltage being of a relatively low electrical potential which is insufficient to initiate a discharge through the tube but sufiicient to maintain a discharge once it has been initiated; said starting and operating circuit comprising an inductance, and a quick-acting vacuum relay, said relay comprising an operating coil, an armature, a normally-open contact and a normally-closed contact; means connecting one side of said inductance to one terminal of said tube and to said armature, means connecting the other side of said inductance to said normally-closed contact and to one terminal of said source of voltage, means including a condenser connecting the other side of said inductance to the other terminal of said tube, means connecting the other terminal of said tube and said normally-open contact to the other terminal of said source of voltage, means connecting said operating coil across the source of voltage, said last-named means including a switch, whereby upon depressing said switch said inductance is placed in series with said source of voltage causing a current flow therethrough, and upon releasing said switch said inductance is disconnected abruptly and then shortcircuited, producing during the circuit interruption a relatively high voltage which is impressed across said tube for initiating a discharge therein.

CHARLES J. MULLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,895,361 Zecher Jan. 24, 1933 1,984,489 Mutsaers Dec. 18, 1934 2,046,980 Van Wijk July '7, 1937 2,103,030 Dorgelo Dec. 21, 1937 2,253,184 Lord Aug. 19, 1941 2,270,368 Zecher Jan. 20, 1942 

